Process comprising heat-treating halogenated butyl rubber in the presence of a novolac resin and thereafter curing, and product obtained thereby



United States Patent Delaware No Drawing. Filed Dec. 24, 1959, Ser. No.861,746 14 Claims. (Cl. 260-49) -This invention is concerned with amethod for heat treating a rubbery polymer, and more particularly, it isconcerned with the improved vnlcanizate therefrom.

It is known that a vulcanizate can be made from a copolymer of anisoolefin with a multiolefin, or from the same copolymer which has beenchemically modified to incorporate halogen in its structure. Thesevulcanizates have been prepared by heat treating the rubbery polymer inthe presence of fillers and promoters, e.g., N-ethyl N-nitroso p-nitrosoaniline (Polyac) and N-methyl N-nitroso p-nitroso aniline (Elastopar);cooling the heattreated rubber to a relatively low temperature;incorporating a curing agent with curing at elevated temperatures toform a rubbery vulcanizate therefrom.

In the past, polymethylol phenol resins have been employed as curingagents. However, these resins required a catalyst such as SnCl or FeClfor butyl rubber; or ZnO for halogenated butyl rubber.

It has now been discovered that phenol-formaldehyde resins can be usedas promoters in the heat treating operation, without catalyst oractivator, to provide a vulcanizate therefrom which possesses greatlyimproved tensile strength. Thus, in accordance with one embodiment ofthis invention, a rubbery polymer of halogenated butyl rubber isprepared. This rubbery polymer is subsequently heat treated in thepresence of a phenol-formaldehyde resin in the absence of catalysts.After cooling the heat-treated rubber, curing agents, e.g., tetramethylthiuram disulfide (Tuads) and benzothiazyl disultide (Altax) areincorporated therein, with curing at elevated temperatures ranging from250 to 400 F. to form a hard rubbery vulcanizate therefrom.

The butyl rubber polymer, which is subsequently halogenated in theinstant invention, is prepared by reacting 70 to 99.5 parts by weight,preferably 85 to 99.5 parts, of an isoolefin with 30 to 0.5 parts byweight, preferably 15 to 0.5 parts, of multiolefin. The isoolefin, ingeneral, is a C to 0; compound, e.g., isobutylene or 2- methyl-l-butene.The multiolefin, in general, is a C to C conjugated diolefin, e.g.,isoprene, butadiene, or piperylene. The preferred polymer is obtained byreacting 95 to 99.5% by weight of isobutylene with 0.5 to 5% by weightof isoprene.

Mixtures of monomers, preferably with l to 5 volumes of inert diluent,e.g., methyl chloride, should be cooled to a temperature between 0 and200 C. and it is preferred that the temperature range be between -60 and130 C. The cold mixture is polymerized by the addition of aFriedel-Crafts catalyst, preferably an aluminum halide catalyst in aliquid or dissolved form, in conjunction with vigorous agitation. Theamount of catalyst is generally about 0.15 to 1.0% by weight of themixed olefins.

The polymerization reaction is rapid and the polymer precipitates out ofthe solution in the form of a slurry or flocculent white solid. Thepolymer, which is recovered and dried, has a Staudinger molecular weightbetween 20,000 and 150,000, preferably 45,000 to 60,000; and

an iodine number between 0.5 and 50, preferably between 1 and 15. Thepreparation of this copolymer is described in US. Patent No. 2,356,128,which is incorporated herein by reference.

The butyl rubber, heretofore described, is halogenated by a substitutionreaction to incorporate at least 0.5 weight percent, preferably about1.0 weight percent, of combined halogen but not more than X weightpercent fluorine or chlorine, or not more than about 3X weight percentcombined bromine or iodine therein, in accordance with the followingequation:

wherein L=mole percent of the multiolefin in the polymer M =molecularweight of the isoolefin M =molecular Weight of the multiolefin M =atomicweight of a halogen In other words, there should he at least about 0.5weight percent of combined halogen in the polymer but not more thanabout one atom of combined fluorine or chlorine or chlorine or 3 atomsof combined bromine or io dine per double bond in the polymer.

The halogenation is generally conducted between about --50 C. and about200 C., and preferably between 20 and 50 C.; however, the temperature isdependent upon the particular halogenating agent which is used. The timeinterval is usually within the range of one minute to several hours,e.g., 3 minutes. The pressure may vary from 0.5 to 400 p.s.i.a.;however, atmospheric pressure is preferred. It is desirable tohalogenate the butyl rubber copolymer while it is dissolved in a C to Chydrocarbon, a C to C halogenated hydrocarbon, carbon tetrachloride,chloroform, hexane, benzene and/or chlorobenzene.

Suitable hal-ogenating agents which may be employed are gaseouschlorine, liquid bromine, iodine monochloride, hydrogen fluoride, alkalimetal hypobromites or hypochlorites, sulfur bromides or chlorides,bromoor chloro-hydantoins, N bromosuccinirnide, and other commonhallogenating agents.

The resulting halogenated butyl rubber polymer may be recovered byprecipitating with an alcohol, acetone or any other non-solvent, andsubsequently drying at a temperature between 0 and 180 C. within apressure range from 1 to 760 mm. of Hg. Other methods for recovering thehalogenated butyl rubber polymer from the hydrocarbon solution areconventional spray and drum drying techniques.

Alternatively, the solution with the halogenated rubbery polymer thereincan be injected into a vessel which contains steam and/or agitated hotwater. The temperature must be high enough to flash off the solventwhereby an aqueous slurry halogenated butyl rubber is formed therefrom.The halogenated butyl rubber is subsequently separated from this slurryby filtration. After a drying step, the polymer is recovered as a crumb,a dense sheet, or a slab, depending upon the milling and extrudingprocedures which are used.

The halogenated copolymer generally has a viscosity average molecularWeight between about 50,000 and 4,000,000. The mole percent unsaturationis usually between 0.5 and 15.0, preferably 0.6 and 5.0..

In accordance with this invention, the halogenated butyl rubber is heattreated with a resol or novolac type substituted phenol-formaldehyderesin. These resol type resins, which are heat-reactive, are generallyprepared by reacting a para-substituted or meta-substituted phenol withan excess of formaldehyde in the presence of a strong alkaline catalyst,e.g., an alkali metal hydroxide. The preparation of resol and novolacresins are well known and are described in many texts, e.g. ExperimentalPlastics and Synthetic Resins by G. F. DAlelio and Phenoplasts by T. S.Carswell. Generally, a mixture of the phenol, formaldehyde and alkalinecatalyst is heated at a temperature between 25 and 100 C. to form aphenol methylol, e.g., parasubstituted 2,6-dimethylol phenol. Thismaterial can be isolated by acidification and separation of the oilylayer. A higher molecular weight can be formed by heating the product ata temperature between 75 and 175 C. The reaction can be carried past themonomer stage to the resinous stage whereupon the mixture is neutralizedand water is removed to give the resinous material. The compounds withinthe purview of the instant invention are formaldehyde reaction productsby alkaline or acid catalysis with: octyl phenol; methyl phenol;tertiary butyl phenol; dodecyl phenol; phenyl phenol; benzyl phenol;(alpha,alpha-dimethylbenzyl) phenol; and cyclohexyl phenol. Thesubstituted phenol formaldehyde resins which are reactive, unreactive orhalogenated are generally incorporated within a range of 0.1 to 25parts, preferably 1 to parts by weight per 100 parts of rubber (phr.).

It should also be noted that the halogenated butyl rubber can also beheat treated with the novolac type resin which is unreactive. Thistherefore includes a phenolformaldehyde resin of the type that iscapable of being converted by heat to the permanently infusible state inthe presence of formaldehyde, or a methylene-yielding curing agent ofthe type commonly used for curing phenolic resins, such ashexamethylene-tetramine or para-formaldehyde. Such phenolic resins areof the novolac type as distinguished from the inherently heat-reactiveresol type previously described as preferred reagents for theprereaction of the butyl rubber. The novolac resins are not dimethylolphenols and they are made by limited condensation of phenol withformaldehyde usually in the presence of an acid catalyst, the ratio ofphenol to formaldehyde in the reaction mixture being maintained highenough so that the formaldehyde present reacts to form essentially onlylinear polymer chains with the phenol, there being insuflicientformaldehyde to form cross-links between the polymer chains, which wouldresult in an infusible, insoluble product. The novolac type of resin isinsoluble in water and is distinguished from the resol type Which isusually prepared in an alkaline medium, using larger quantities offormaldehyde. The novolacs are distinguished by the fact that,practically speaking, they are permanently fusible and soluble and donot harden upon being heated unless a curing agent in the form ofadditional formaldehyde is added. Preferably the phenolic resin is onewhich has been modified with cashew nut shell oil. Such modifiedphenolic resins are well-known commercially available materials, astypified by the resin sold under the trade-designation Durez No. 12686,which is made from cashew nut shell oil and a lower molecular weightphenol. Frequently the commercial form of the resin already contains asuflicient quantity of a methylene-yielding curing agent to render itheat-hardenable, as in the case of the material sold under thetradedesignation Durez No. 12687, which is believed to be a mixture of92 parts of cashew nut shell oil modified phenolic resin and 8 parts ofhexamethylenetetramine. Other commercially available cashew nut shelloil modified phenolic resins, containing a curing agent, are thematerials known in the trade as Varcum 9820 and Varcurn 9831. If theresin does not already contain a formaldehyde-yielding substance, from 1to 12 parts of such substance should be added to the mixture, per 100parts of the halogenated butyl rubber.

In the present invention the reactive, unreactive or halogenated resinis heat treated with halogenated butyl 3, rubber in the absence" ofcatalysts such as ZnO, Zrn stearate, ZnCl Z nB r Feclg, and SnCl If heattreatedwith the halogenated butyl rubber i111 this invention, thehalomethyl hydrocarbon-substitutedi phenol curing agents are provided byhalogenating the; above polymethylol phenols, e.g., 2,6-dimethylolparasubstituted phenols, either in the monomeric or poly-- meric form,to at least partially substitute halogen for the hydroxyl portionofthemethylol groups; or by the: controlled halogenating of theafore-mentioned methyloll containing resins prepared by the condensationof an alI-- dehyde with a substituted phenol having the twoorthorpositions unoccupied. This halogenation is generally per formed ata temperature between 0 and 150 C., preferably between 20 and C. Thehalogenating agents; which are suitable for the present invention aregaseous: hydrogen fluoride, hydrogen chloride, hydrogen bromide,hydrogen iodide, gaseous chlorine, liquid bromine, alkali metalhypochlorites or hypobromi t'es, concentrated aque-- ous hydrogen iodinesolutions, C to C tertiary alkyli hypochlorites, sulfur bromides,sulfuryl chloride, pyridinium chloride perchloride, N-bromosuccinimide,alpha-- chloroacetoacetanilide, N,N'-dichloro-5,5 dimethylhy-- dantoin,iodine halides, trichlorophenol chloride, N-- chloroacetamide,beta-bromo-methyl phthalimide, etc.. The preferred halogenating agentsare gaseous hydrogen: fluoride, hydrogen chloride, hydrogen bromide,hydrogen iodide, and chlorine. Generally the polymethylol com-- pound orresin is halogenated in the presence of an inert; organic solvent, e.g.,hexane, benzene, chloroform, or carbon tetrachloride by forming a 20 to50 wt. percent: solution which is subsequently contacted with ahalogenat ing agent for a few minutes up to several days, depending.upon the reactivity of the specific halogenating agent- The amount ofhalogenating agent employed will vary from 0.3 to 4 moles per mole ofpolymethylol phenol and the halogenated polymethylolhydrocarbon-substituted phenol can contain from 1 to 60 wt. percent ofcombined halogen. The monomeric form of these compounds can berepresented by the following general structure:

XHgC- CHzX wherein R is an alkyl, aryl, or alkaryl hydrocarbon con--taining 4 to 16 carbon atoms located in the meta or para. position (4-5position): X is a halogen such as fluorine, chlorine, bromine, oriodine; and Y is hydrogen or by droxy. This therefore includes thefollowing compounds: 2,6-dichloromethyl-4-tertiarybutyl phenol,2,6-dichloromethyl-4-octyl phenol, 2,6-diiodomethyl 4 dodecyl phenol,2,6-dichloromethyl 4 phenyl phenol, 2,6-dibromomethyl 5 pentadecylphenol, 2,6-dibromomethyl-- S-pentadecyl resorcinol and2,6-dibromomethyl 4 cumyl phenol. If desired, these compounds may beblended with unreactive or reactive polymethylol compounds or resins toobtain a composition having the desired curing: rate.

In addition to the substituted phenol formaldehyde resin as a promoter,the halogenated rubbery copolymer can also be heat treated with othercompounding ingredients such as mineral fillers, e.g., hydrated silicaand 2,2- methylene (4-methyl-6-tertiary butyl) phenol (Antioxidant2246). The heat treating operation can be performed statically;dynamically, e.g., hot milling; or with intermediate combinations ofalternate or cyclic static heating followed by a short interval ofmastication. The heat treatment temperature is generally within therange of 200 to 450 F., preferably from 200 to 350 F. The time isinversely dependent upon the temperature, and

ranges from 1 to 8 hours with static heating at 250 F., and ranges from1 to 30 minutes with dynamic heating at 200 to 350 F.

The heat treatment should be terminated with a final properties of eachvulcanizate were determined as shown herebelow:

30 MINUTE CURE mastication and/ or mixing to provide a mixture which is5 Physical Properties A B O homogeneous and is in a smooth workablecondition.

The heat-treated rubbery mixture is subsequently cooled Tensile Strength(PM) 1, 975 27305 2, 470 to a temperature below 200 F. in order toincorporate Elongation (Percent)- 700 655 675 curing agents withoutscorching occurring therein. These Show Hardness 54 50 50 curing agentsare generally added at a temperature be- 10 tween 100 and 150 F. Theusual curing agents are 0.5 60 MINUTE CURE to 3 parts of sulfur phr.;0.5 to 5 parts of accelerators phr.,

e.g., tetramethyl thiuram disulfide, Z-mercaptobenzothia-PhysicalPmPerties A B G zole, benzothiazole disulfide,bis-4-ethylthiazole disulfide,

ip guanidine, y d hy -a e products, zinc @fgjlgfiifglilggfit I 9g 3%?2g2 dimethyldithiocarbamate, thiazole guanidine, aldehyde- ShoreHardness 57' 47 50 amines, thiazolines, imidazolines, thioureas, anddithiols.

Other compounding agents, which may be incorporated into the heattreated rubbery mixture after it has been Example H cooled, includenon-sulfur curing agents such as p-di- The halogenated rubbery copolymerof Example I was nitrosobenzene, p-quinone dioxime, polyhydroxyaromacompounded with the following ingredients to eventually tics, andpolyamines; antioxidants and stabilizers, e.g., form vulcanizates E, Fand G:

stearic acid; zinc oxide; pigments and/or dyes; processing aids, e.g.,waxes, resins and/ or oils; extenders, e.g., non- Phn volatile mineraloils and/or esters. Compound After the curing agents and othercompounding agents E F G have been incorporated in the heat-treatedrubbery polymer, the composition therefrom is extruded or molded intoHaiogenated Rubbery oopolymel. 100 100 100 any desired form. Theextruded admixture is subse- Antioxidant 2246 1 1 1 quently cured byheating to a moderate temperature be- 30 233 3 3 tween 250 and 270 F.for 240 to 60 minutes, or by heatt a a id 1 1 1 ing to a relatively hightemperature between 300 and fi ggigl 3 400 F. for 5 to 0.5 minutes.

Thus, in accordance with this invention, a vulcanizate is formed has arelatively physical trength T1115 compounded rubber, 01' Without theT6511]. thereand therefore it can be used in applications requiring iminas a Pmmoter, was heated directly in E1 struthers'wens proved resistanceto prolonged exposure to steam and ml'XeI' at a temperature 0f 3000 RAll ingredients hot water. Experience h shown th t imprgvemgnts includedwithin 2.5 minutes and the heat treatment was are also found in steamand hot Water hose applications. Conducted Within 8 millutes- Themat-treated Polymer Furthermore, when a phenol formaldehyde resin isused 49 Was then cooled to a temperature of and the as a promoter in theheat-treating operation catalysts do lowing curatives were incorporatedtherein on cold not have to be present in the operation mill: 1 parttetramethylthiuram disulfide, 2, parts benzo- The following examples aresubmitted to illustrate and thiazyl disulfide, and 3 parts ZnO phr. Theheat-treated not to limit this invention. polymer with the curativestherein were subsequently Example I cured at a temperature of 307 F. foreither 30 or 60 minutes. The physical properties of the vulcanizates A rry p lym r w p p comprising therefrom are indicated in the table below:percent of isobutylene with 2.5 percent isoprene. This polymer wasreacted with gaseous chlorine in n-hexane 30 MINUTE CURE as a solvent toincorporate 1.2 ercent of chlorine in its structure by a substitutionreact ion. One hundred parts 50 Physcal Propertles E F G of thehalogenated rubbery copolymer were mixed with the following compoundslisted herebelow: fifjgg ifi fiig gg 2g3 253 Shore Hardness 67 60 59 PM60 MINUTE CURE Compound A B 0 Physical Properties E F G fi g g 1 i l 60iifii ia il ii ilchlliii1:3:I I 333 E33 333 Hi.silb 5Q 0 50 ShoreHardness 62 58 Stearie Acid 1 1 1 Amberol ST-137X n- 3 Ambeml d 5Examples I and II demonstrate that the tensile strength a 2 2, methylene(4 methyl 6 term but 1) henol of a vulcanizate is substantiallyincreased by incorporatb ygmed Silica. y y p 65 ing a substitutedphenol-formaldehyde resin as a promoter gnreaetive phenol formaldehyderesin of Rohm and aas. in the heat treatment of a chlorinated copolymerof is0- eat reactlve phenol formaldehyde resin of Rohm and Haas.butylene with isoprenel Furthermore, it is unexpected that the heattreatment can be performed in the absence These admixtures were placedon a 6-inch roll mill at a f Z o at these temperatures i Such relativelyShort temperature of for 10 minutes- The heat-trefltfid times. Inaddition, it is surprising that the unreactive rubbery P0131111ertherefrom Was cooled to a temperature phenol-formaldehyde resin not onlyis efiective but also Of 80 F. and 1 part Of tetramethylthiuramdiSUlfidB, 2 is superior to the reactive type resi parts of benzothiazyldisulfide and 3 parts of Zinc oxide were incorporated therein. Thiscomposition was cured Example for either 30 or 60 minutes at 320 F. andthe physical The halogenated copolymer of Example I was com- MistronVapor Talo.

pounded with the following ingredients to eventually form vuloanizatesH, I, and J:

These admixtures were placed on a 6-inch roll mill at a temperature of290 F. for minutes. The heattreated rubbery polymer therefrom was cooledto a temperature of 80 F. and 1 part of tetramethyl thiuram disulfide, 2parts of benzothiazyl disulfide, and 3 parts of zinc oxide wereincorporated therein.

In addition to these curatives, 3 phr. of Amberol ST- 137X was added tovulcanizate I during the finalizing process (i.e., with curatives afterthe heat-treating process).

These compositions were cured for 60 minutes at 307 F. and the physicalproperties of each vulcanizate were determined as shown herebelow:

Vulcanizate I shows the pronounced improvement that can be obtained inphysical properties by using the phenolformaldehyde resin as aheat-treating promoter without an activator. The tensile strength is farsuperior to that of vulcanizate I in which the polymethylol-phenol resinis used as a curative With the ZnO activator.

Example IV The halogenated copolymer of Example I was compounded withthe following ingredients to eventually form vulcanizates K and L:

Compound Halogenated Rubbery Copolyrner M O g Antioxidant 2246 AmberolST-137X Stearie Acid Compound K Was subsequently heat treated on a 6-inch roll mill at 300 F. for 10 minutes and then cooled PhysicalProperties K L Tensile Strength, (p.s.i.) 1, 645 1, 470 Elongation 745745 Vulcanizate K shows that the heat-treating process of this inventionis also effective in other fillers such as talc.

Example V The following recipe was provided in conjunction with curingsimilar to Example III:

Compound M N O Cure, 307 F./60. Tensile Strength. Elongation Copolymerof Example I. b A bromo-resin.

This example indicates that a halogenated phenolformaldehyde resin canbe employed in the present invention.

Having described the general nature and physical embodiments of thepresent invention, the true scope is now particularly pointed out in theappended claims.

What is claimed is:

l. A method which comprises preparing a rubbery copolymer of a majoramount of an isoolefin with a minor amount of a multiolefin which hasbeen modified to incorporate a halogen therein; heat treating 100 partsof said copolymer in the presence of 1 to 25 parts of a novolac acidcatalysed phenol-formaldehyde resin in the absence of catalysts selectedfrom the group consisting of ZnO, ZnCl ZnBr FeCl SnCl and Zn stearate ata temperature between 200 and 350 F.; cooling said heattreated copolymerbelow 150 F and curing said cooled heat-treated copolymer at atemperature between 250 and 400 F. to provide a vulcanizate therefromwith improved physical properties.

2. The method according to claim 1 in which the halogenated rubberycopolymer has chlorine incorporated in its structure.

3. The method according to claim 1 in which the halogenated rubberycopolymer has bromine incorporated in its structure.

4. The method according to claim 1 in which the rubbery polymer is thecopolymer of isobutylene with isoprene.

5. The method according to claim 1 in which 100 parts of the rubberycopolymer are heat treated with 1 to parts of the resin.

6. The method according to claim 1 in which the curing is performed inthe presence of tetramethyl thiuram disulfide and benzothiazyldisulfide.

7. A composition which has been prepared by providing a rubbery polymerof a major amount of an isoolefin with a minor amount of a multiolefinwhich has been modified to incorporate a halogen in its structure; heattreating 100 parts of said polymer in the presence of 1 to 25 parts of anovolac acid catalyzed phenol-formaldehyde resin in the absence ofcatalysts selected from the group consisiting of ZnO, ZnCl ZnBr FeClSnCl and Zn stearate at a temperature between 200 and 350 F.; coolingsaid heat-treated rubbery copolymer at a temperature below F. and curingsaid cooled polymer at a temperature between 250 and 400 F. to provide avulcanizate therefrom with increased strength.

8. The composition according to claim 7 in which the halogenated rubberypolymer has chlorine incorporated in its structure.

9. The composition according to claim 7 in which the halogenated rubberypolymer has bromine incorporated in its structure.

10. The composition according to claim 7 in which the polymer is thecopolymer of isobutylene with isoprene.

11. The composition according to claim 7 in which 100 parts of therubbery polymer are heat treated with 1 to parts of the resin.

12. The composition according to claim 7 in which the curing isperformed in the presence of tetramethyl thiuram disulfide andbenzothiazyl disulfide.

13. A method which comprises preparing a rubbery copolymer of 97.5%isobutylene with 2.5% isoprene which has been modified to incorporate1.2% chlorine therein; heat treating 100 parts of said copolymer in thepresence of 1 part 2,2-methylene (4-methyl-6-tertiary butyl) phenol, 4parts of MgO, 50 parts of hydrated silica, 1 part of stearic acid, and 3parts of novolac acid catalyzed phenol-formaldehyde resin and in theabsence of ZnO at a temperature of 300 F. for 8 minutes; cooling saidheattreated rubbery copolymer to a temperature of 80 F.; and curing saidcooled polymer at a temperature of 307 F. for 60 minutes in the presenceof 1 part tetr-amethylthiuram disulfide, 2 parts of benzothiazyldisulfide, and 3 parts ZnO to provide a vulcanizate therefrom with atensile strength of 1800 p.s.i.

14. A composition which has been prepared by providing a rubberycopolymer of 97.5% isobutylene with 10 2.5% isoprene which has beenmodified to incorporate 1.2% chlorine therein; heat treating 100 partsof said 00- polymer in the presence of 1 part 2,2'-methylene (4-methyl-6-tertiary butyl) phenol, 4 parts of MgO, parts of hydratesilica, 1 part of stearic acid, and 3 parts of novolac acid catalyzedphenol-formaldehyde resin and in the absence of ZnO at a temperature of300 F. for 8 minutes, cooling said heat-treated rubbery copolymer to atemperature of 80 F.; and curing said cooled polymer at a temperature of307 F. for minutes in the presence of 1 part tetramethylthi-uramdisulfide, 2 parts of benzothi-azyl disulfide, and 3 parts ZnO toprovide a vulcanizate therefrom with a tensile strength of 1800 p.s.i.

References Cited in the file of this patent UNITED STATES PATENTS2,701,895 Tawney et al Feb. 15, 1955 2,702,287 Iknayan et a1 Feb. 15,1955 2,788,839 Kindle et al Apr. 16, 1957 2,839,443 Fleming June 17,1958 2,857,357 Smith Oct. 21, 1958 2,955,102 Clayton et al Oct. 4, 1960

13. A METHOD WHICH COMPRISES PREPARING A RUBBERY COPOLYMER OF 97.5%ISOBUTYLENE WITH 2.5% ISOPRENE WHICH HAS BEEN MODIFIED TO INCORPORATE1.2% CHLORINE THEREIN; HEAT TREATING 100 PARTS OF SAID COPOLYMER IN THEPRESENCE OF 1 PART 2,2''-METHYLENE (4-METHYL-6-TERTIARY BUTYL) PHENOL, 4PARTS MGO, 50 PARTS OF HYDRATED SILICA, 1 PART OF STEARIC ACID, AND 3PARTS OF NOVOLAC ACID CATALYZED PHENOL-FORMALDEHYDE RESIN AND IN THEABSENCE OF ZNO AT A TEMPERATURE OF 300* F, FOR 8 MINUTES; COOLING SAIDHEATTREATED RUBBERY COPOLYMER TO A TEMPERATURE OF 80* F, AND CURING SAIDCOOLED POLYMER AT A TEMPERATURE OF 307* F, FOR 60 MINUTES IN THEPRESENCE OF 1 PART TETRAMETHYLTHIURAM DISULFIDE, 2 PARTS OF BENZOTHIAZYLDISULFIDE, AND 3 PARTS ZNO TO PROVIDE A VULCANIZATE THEREFROM WITH ATENSILE STRENGTH OF 1800 P.S.I.